I also dislike it, but I guess it was done to be consistent. They are the hero nicknames, like Saitama's Bald Cape, or whatever it was. Genos was Demon Cyborg, if I remember correctly. There would be lots of heroes whose hero names would be meaningless to non-Japanese speakers if they were left untranslated. Honestly, if I had needed to make a professional decision about it, I might have gone with translations as well. It's a tough spot to be in.